Moved:UGMS
SCEC Committee for Utilization of Ground Motions Simulations
Contents
Goal and Charter
The SCEC Committee for Utilization of Ground Motions Simulations (or "UGMS Committee" for short) was chartered the SCEC Earthquake Engineering Implementation Interface Focus Group.
The SCEC UGMS Committee is tasked to develop long-period response spectral acceleration maps for Los Angeles region for inclusion in NEHRP and ASCE 7 Seismic Provisions and in Los Angeles City Building Code. The maps would be based on 3-D numerical ground-motion simulations, and ground motions computed using latest empirical ground-motion prediction equations from the PEER NGA project. This project is coordinated with (1) the SCEC Ground Motion Simulation Validation Technical Activity Group (GMSV-TAG), (2) other SCEC projects, such as CyberShake and UCERF, and (3) the USGS national seismic hazard mapping project.
Committee Members
- Norm Abrahamson (PG&E/UCB)
- John Anderson (UNR)
- Bob Bachman (R.E. Bachman Consulting Structural Engineers)
- Jack Baker (Stanford)
- Jacobo Bielak (CMU)
- C. B. Crouse (URS, chair)
- Art Frankel (USGS)
- Rob Graves (USGS)
- Ron Hamburger (SGH)
- Curt Haselton (CSUC)
- John Hooper (MKA)
- Marty Hudson (AMEC)
- Charlie Kircher (Kircher & Associates)
- Marshall Lew (AMEC)
- Nico Luco (USGS)
- Farzad Naeim (Farzad Naeim, Inc.)
- Paul Somerville (URS)
In the future the UGMS Committee plans to invite structural engineers (SE’s) in Southern CA to participate as Corresponding Members. Possibilities include SE’s from the City of L.A., L.A. County, and Structural Engineers Association of Southern California (SEASC). The addition of these SE’s is important for building a consensus on the long period ground motion maps for the Los Angeles region.
Participating Organizations
Besides SCEC, the Federal Emergency Management Agency (FEMA) and USGS Golden, Colorado, office would participate. FEMA would enter the project during the next NEHRP code cycle, which would likely begin in late 2015. The USGS would prepare the long period maps and submit them to the Provisions Update Committee (PUC). The PUC membership would be established by the organization responsible for preparing the NEHRP seismic provisions. FEMA will select this organization, which in years past, has been the Building Seismic Safety Council of the National Institute of Building Sciences. The SCEC pilot study would then also become an Issue Team project under the PUC with the specific goal of developing the long-period maps for the Los Angeles region. If the PUC approves the maps and they become part of the NEHRP seismic provisions, then the maps would be submitted to the ASCE Seismic Subcommittee for possible inclusion in the ASCE 7 standard.
Accomplishments
2013
The 1st-year scope consisted of one 2-hour meeting (3 – 5 p.m.) at SCEC on April 3, 2013; the meeting was held in conjunction with the GMSV-TAG committee meeting earlier in the day. The 1st meeting covered the following agenda items: (1) finalize committee membership, (2) establish technical tasks and the resources to accomplish these tasks, (3) create organization chart and identify the committee members to lead and participate in each task, and (4) establish a schedule for the project.
2014
The second UGMS meeting was held on May 12 at SCEC. Much of the meeting was devoted to a discussion of the CyberShake platform for generating ground-motion simulations throughout Southern California. T. Jordan first presented an overview of CyberShake and the SCEC ground motion simulation program. Jordan followed with presentations on the SCEC community velocity models, and comparisons of ground-motion predictions from CyberShake and the empirical NGA equations. Jordan also showed that Cybershake was able to reproduce long period ground motions from recent local earthquakes. Jordan’s final presentation was plans for future CyberShake development, which included extending the frequency band to 1.3 Hz to better define 1-sec period motions.
The UGMS affirmed that the long period mapping project will proceed on two parallel tracks, in which PSHA/DSHA will be conducted from the 3-D numerical simulations using CyberShake and from the traditional empirical approach using the NGA-West equations. It was agreed that the results from the 3-D simulations could be used to refine the equations ultimately used in the empirical approach. The second meeting concluded with an action item that SCEC would generate long period response spectra at selected sites using CyberShake and the NGA-West equations as a benchmark to guide the future direction of the committee.
Fourteen (14) sites were selected throughout Southern CA (see attached map) and risk targeted Maximum Considered Earthquake (MCER) response spectra were computed at each site by following the procedures in ASCE 7-10. Plots of the probabilistic and deterministic MCER response spectra, as well as the resulting MCER response spectra (lower of the probabilistic and deterministic MCER) were presented at the third UGMS committee meeting on November 3 at SCEC. Each plot showed the MCER response spectra from CyberShake and NGA-West. For some sites the two spectra were similar and at other sites significant differences were observed. The observations were discussed and suggestions for the third year research program were proposed.
2015
In progress: The reasons for the similarities and differences in the response spectra at the 14 sites will be investigated during the first half of 2015. Possible limitations of both the NGA and CyberShake models will be explored. Sensitivity studies using CyberShake will also be conducted including the effects of the shallow velocity structure and alternative source models. The CyberShake MCER response spectra the 14 sites confirmed that the spectral ordinates were underestimated at 2-sec period, the present lower limit of the period band the current CyberShake modeling. Thus, in the first half of the third year, SCEC will expand the valid period range of CyberShake to eliminate the underestimation at 2-sec period.
Prior to the 4th UGMS meeting, scheduled for the spring, SCEC will conduct sensitivity studies to investigate the following:
- effect of the background seismicity on the response spectra at the shorter natural periods ~2 sec, and
- effect on the response spectra due to variations in the (a) shallow velocity structure at selected sites, and (b) earthquake source model.
During the 4th meeting, the results of these items will be discussed and conclusions drawn on the comparisons of the CyberShake and NGA-West MCER response spectra at the 14 sites and other selected sites. The UGMS will also discuss progress and schedule to extend the CyberShake model to obtain reliable ground-motion response spectra down to 1-sec period. Also, during the 4th meeting, specific direction for the UGMS committee for the remainder of 2015 will be identified, and a 5th meeting will be planned for the fall.
At the time of the 5th meeting, the schedule for the next seismic code cycle should be known, and it will dictate the schedule of the UGMS for developing and submitting a proposal to the PUC for long period MCER maps of the greater Los Angeles area. Also, a clearer direction on the specific approach for developing long period maps is a target outcome of the third year.
During 2015 selected members of the UGMS plan to contact city building officials in Southern California (e.g., cities of Los Angeles, Long Beach, San Bernardino) and brief them on our project and obtain their input on the possibility of providing long period ground-motion maps for the region as amendments to the ground-motion maps that will appear in ASCE 7-16, to be published in 2016. If the reception is favorable, then the schedule for preparing the maps would be established.
The other mapping issue that the UGMS will be addressing is the approach for developing maps proposed for the ASCE 7-22 standard, scheduled for release in 2022, and the coordination of this activity with the USGS Golden, Colorado, office.
Committee Meetings
- April 3, 2013
- May 12, 2014
- November 3, 2014
